Dear Dr. Bennett, I would like your help with a young horse I have been massaging every couple of weeks. He is 2 1/2 on pasture and his owner works with him about 15-20 minutes once a week or so on leading, stopping, tying to the trailer, from what I have seen very careful and no sidereins or surcingle.

Recently the horse started exhibiting very specific and repetitive sweat patterns at rest in the pasture on both shoulder though the left shoulder is more pronounced. The sweat marks are very localized, two rectangular spots with the point pointing toward the horse's head about a hand from each other on the surpaspinatus and spine of the scapula border.

A few years ago, I did some research for another owner who had a horse with a similar pattern on one shoulder and I found some information about this possibly being a dysfunction of the
peripheral nerves in that localised area, a dysfunction
of the autonomic nervous system caused by either trauma to the nerve and/or an impingement of it. I was never able to ascertain if this was correct with the vet and while I have recommended this client speak to her vet, I wanted to know if you had seen this before and what your thoughts are. I have permission to post images but they are a bit too big, if I can send them separately I would be happy to do so.

I, too, would be interested in your thoughts, Dr Deb, on this phenomenon. My grey anglo-arab, who you have seen in photos on other threads, has a similar patch of abnormal sweating on his right shoulder, which started appearing about 4 months ago.

It is roughly 3" long and about 3/4" wide and runs along the anterior border of the supraspinatus muscle about a a third of the way down its length.

I will try to get a photo too.

When not sweating, the patch is very faintly visible, looking slightly darker, and it starts to sweat as soon as he becomes warm or not OK.

I have asked a variety of vets and body workers, none of whom have any explanation. Caroline, my thoughts are similar to yours in that it is either a local disruption to the thermoregulatory system, but why should this happen? or it is due to a deeper dysfunction of the autonomic nervous system, but again, why?

Yes, these are all good examples. I was looking around through my files, but failed to find, a photo I took of a horse many years ago whose 'localized sweat patch' was two palms broad. The patches are always upon the shoulders or neck, so far as I know; I've never seen one on a horse's thigh or the top of the butt.

As to their exact cause, I've been looking around through the literature on that too, and the best I can come up with is a note from Matthew Mackay-Smith in a very old issue of Equus Magazine. Dr. Matthew was asked this in the 'letters to the editor' column and his reply was that it was indeed due to some small dysfunction in the autonomic nervous response which controls sweating as well as sebaceous secretion.

The pattern of the patches is suspiciously reflective of the dermatome pattern. 'Dermatomes' are zones of the skin, which are like invisible zebra stripes, each of which is innervated by peripheral branches coming off from between whichever pair of vertebrae is directly above them. You can see the dermatome pattern if you look it up in Sisson & Grossmann.

Horses who manifest these patches are not ill or off or dysfunctional in any other way, and I think that even if it is due to nerve damage, the damage must be minor. Nor may we automatically assume that such nerve damage is caused by 'pinching', i.e. mis-posturing, or by something like a mis-fitting saddle; it could as readily be due to nutritional deficiency, ingestion of toxic substances, or the action of a virus.

I'll continue to keep my eye out for published research on this subject, and anyone else who comes across anything, do please let us know about it. -- Dr. Deb

Thank you very much for you answer. Do you have any suggestions for returning the horse to his previous condition where this was not happening?
If its dermatone would it be then related to the first or second thoracic vertebra based on the position of the spots? I am thinking perhaps I can try a little myofascial release in the event there is nerves restricted? I will see the horse wed and will take more pics.

Caroline, "dermatome" is not a cause of injury or dysfunction; it is a bodypart. Please take the time to go look up the concept and the very clear diagram presented in Sisson & Grossmann's "Anatomy of the Domestic Animals". You might also follow this up by Googling "dermatome", which will bring up the diagram as for human anatomy.

As to treatment: you can try your modality and see what effect it has. It will be interesting to see whether, by the application of myofascial release or any other technique or therapy, any change is actually created. As I mentioned before: we do not have to assume, and indeed it is probably inadvisable to assume, that this is due to any amount of "pinching" of any nerve; as I said previously, it could just as readily be due to the action of toxins or a virus.

I will and I will share your feedback with the owner. The horses moved to a new location this week so if it was a toxin or a virus linked to the environment would a change of location possibly make a change?

I will read up on dermatone and give you progress reports. Thanks for the reco on book/googling.

I have come across one horse in my Chiropractic practice some years ago with a similar sweat patch, though this was over the thoracic paraspinal muscles at about T15 / 16 on one side only, and was directly connected with trauma. This did reduce and finally resolve either with the help of Chiropractic, or in spite of it!

Solo is currently having some acupuncture, so I will let you know if it makes any difference.

So the horse today and experimented with a variety of touches. What made a difference was a fairly energetic "waking up" of the whole area, not focusing on the spots themselves. Initially I thought perhaps the heat from my fingers must have been drying them a little but even avoiding them and working around them they dried up quite a bit. I cant imagine this would have made a long lasting difference but I will see him next week and play with it again. Lovely, soft and gentle horse, a joy to touch.

i have a 8 year old t.b mare that has a 1 1/2 foot long patch ( and growing )down her right hip. very wierd. and i see know as i read here i guess i should not worrie. it is very weird but dose not bother her. my email is shecutsit@yahoo.com if any one has any more info i would appreciate it

Hello, this was always very interesting to me... I had a 4 yr. old TB mare that did this on her hips (both sides perfectly symmetrical) also, on her shoulders... I of course did hours of research but couldn't find anything that seemed to fit the description... at the time I wrote it off as her being "nervous" (even though she didn't seem like it)...

I do body work now and work a lot with mineral imbalances... most of the horses I see with these unusual sweat marks I consider on toxic overload... of course that is the best description I have and a toxin test would confirm. But, regardless, it seems to mysteriously disappear when the minerals are re-balanced and the liver is cleaned out... maybe it was shear coincidence, but it seems like with the environment that we live in now a days being imbalanced and toxic our bodies are just doing the best they can... I guess after a while it all just builds up and comes to a head... come to think of it, she did absess 2 times in 6 months...

In my simple thought process, I like to think that whatever we see on the outside of the horse (puss, ooze, diarrhea, sweat) is a reflection (sometimes symptom) of what is on the inside... please correct me if this is ignorant.

For the last year my horse has a patch of skin about 3" x 5" on his left pectoral muscle sweat profusely every single time he was ridden even if he never broke a sweat anywhere else on his body.
I asked my ostepath about it and she said it was a 'myotome'.
I never got a chance to talk about it in detail with her so I dont even know what a myotome is other than it has to do with nerves but I thought it was worth mentioning especially because the one time treatment she performed made the problem disapear completely.